Estimating regional fluxes of CO2 and CH4 using space-borne observations of XCH4 : XCO2
Estimating regional fluxes of CO2 and CH4 using space-borne observations of XCH4 : XCO2
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DOI：
10.5194/acp-14-12883-2014
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发表时间：
2014-01-01
影响因子：
6.3
通讯作者：
Langenfelds, R. L.
中科院分区：
文献类型：
--
作者：
Fraser, A.;Palmer, P. I.;Langenfelds, R. L.
我们使用GEOS-Chem全球3-D大气化学传输模式来解释从日本温室气体观测卫星（GOSAT）检索的XCH 4：XCO 2柱比。这些数据的优势，CO2和CH 4列检索独立使用一个完整的物理最佳估计算法是，他们不太容易散射相关的区域偏见。我们表明，该模型能够重现观察到的全球和区域空间（平均偏差= 0.7%）和时间变化（全球r（2）= 0.92）的这一比例与模型偏差<2.5%。我们还表明，这些变化是由二氧化碳和甲烷的排放量，通常是6个月的阶段，这可能会降低敏感性的比率变化的气体。为了同时估计CO_2和CH_4的通量，我们采用了极大似然估计法。我们利用GOSAT观测数据XCH_4：XCO_2，采用了两种方法来求解这两种气体的独立通量估计：（1）CO_2和CH_4之间的先验误差协方差，描述了生物质燃烧的共同源;以及（2）还拟合了提供额外约束的CH 4和CO2摩尔分数的独立地面大气测量，提高了观测到的GOSAT比率约束通量估计的有效性。我们使用数值实验证明了这两种方法的影响。仅使用GOSAT比值并利用生物质燃烧引起的误差协方差推断的后验通量估计与我们实验中的时间通量不一致，因为反演系统无法判断调整哪些物种的通量。这反映了XCH 4：XCO 2对生物质燃烧的弱依赖性。我们发现，添加的表面数据有效地提供了一个“锚”的反演，显着提高了GOSAT比率的能力，以推断CH 4和CO2通量。我们表明，从GOSAT XCH 4推断的区域通量估计：2010年期间的XCO 2比率和表面摩尔分数数据通常与从拟合XCH 4或全物理XCO 2数据产品推断的相应值一致或更好，作为判断的后验不确定性，我们表明，从比率测量推断的通量执行最好的地区，有一个大的季节性循环，如热带南美洲，我们报告了一个小，但显着的年度来源的CO2相比，一个小的年度汇推断从XCO 2数据。我们认为，考虑到比测量是由系统误差比完整的物理数据产品，由此产生的后验估计和不确定性提供了一个更忠实的描述的tmth。根据我们的分析，我们还认为，通过使用的比率，我们可能会达到目前的限制，这些观测到的天基数据的精度。
We use the GEOS-Chem global 3-D atmospheric chemistry transport model to interpret XCH4 : XCO2 column ratios retrieved from the Japanese Greenhouse Gases Observing Satellite (GOSAT). The advantage of these data over CO2 and CH4 columns retrieved independently using a full physics optimal estimation algorithm is that they are less prone to scattering-related regional biases. We show that the model is able to reproduce observed global and regional spatial (mean bias = 0.7 %) and temporal variations (global r(2) = 0.92) of this ratio with a model bias < 2.5%. We also show that these variations are driven by emissions of CO2 and CH4 that are typically 6 months out of phase, which may reduce the sensitivity of the ratio to changes in either gas. To simultaneously estimate fluxes of CO2 and CH4 we use a maximum likelihood estimation approach We use two approaches to resolve independent flux estimates of these two gases using GOSAT observations of XCH4 : XCO2: (1) the a priori error covariance between CO2 and CH4 describing common source from biomass burning; and (2) also fitting independent surface atmospheric measurements of CH4 and CO2 mole fraction that provide additional constraints, improving the effectiveness of the observed GOSAT ratio to constrain flux estimates. We demonstrate the impact of these two approaches using numerical experiments. A posteriori flux estimates inferred using only the GOSAT ratios and taking advantage of the error covariance due to biomass burning are not consistent with the tme fluxes in our experiments, as the inversion system cannot judge which species' fluxes to adjust. This reflects the weak dependence of XCH4 : XCO2 on biomass burning. We find that adding the surface data effectively provides an "anchor" to the inversion that dramatically improves the ability of the GOSAT ratios to infer both CH4 and CO2 fluxes. We show that the regional flux estimates inferred from GOSAT XCH4 : XCO2 ratios together with the surface mole fraction data during 2010 are typically consistent with or better than the corresponding values inferred from fitting XCH4 or the full-physics XCO2 data products, as judged by a posteriori uncertainties We show that the fluxes inferred from the ratio measurements perform best over regions where there is a large seasonal cycle such as Tropical South America, for which we report a small but significant annual source of CO2 compared to a small annual sink inferred from the XCO2 data. We argue that given that the ratio measurements are less compromised by systematic error than the full physics data products, the resulting a posteriori estimates and uncertainties provide a more faithful description of the tmth. Based on our analysis we also argue that by using the ratios we may be reaching the current limits on the precision of these observed space-based data.